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Tutorial

Introduction of Electron Configuration

To understand electron configuration, we must understand the importance of electrons and its components.

The Bohr Model of an Atom offers a backbone in understanding electrons and their atomic structure.

Breaking down the structure of an atom, we can further locate electrons of an atom.

There are two methods of notating electron configuration: orbital notation and atomic notation.

To understand how to orbitally notate electron configuration, we must understand the Pauli Exclusion Principle, the Aufbau Principle, and Hund's Rule.

To understand how to atomically notate electron configuration, we must understand the organization of the periodic table and the components of electrons.

The Bohr Model of an Atom

Electron Configuration

Electron Configuration is the arrangement of electrons of an atom.

By understanding an atom's structure, we can understand the location and the arrangement of electrons.

Review of the Atom

Electrons travel on shells. The shells are split into sub-shells. Each sub-shell is made of one or more orbits. There is always an odd number of orbitals in each sub-shell. Each orbital can only have a maximum of two electrons. If there are two electrons in an orbital, then they must have opposite spins.

Review of the Atom

Electron Configuration of the Period Table

The periodic table is divided into blocks according to sub-shells: s (blue), p (green), d (brown), and f (purple) (sub-shells are arranged from the lowest energy shell to the highest energy shell). The sub-shells are determined by the number of periods.

The orbital of the atoms are determined by the periods of the elements. The periods are the rows of the period table.

The number of electrons are determined by the number of boxes in each sub-shell.

Recall, an orbital can only store 2 electrons.

A s sub-shell is made up of 1 orbital. Hence, 1 s orbital can store 2 electrons.

A p sub-shell is made up of 3 orbitals. Hence, 3 s orbitals can store 6 electrons.

A d sub-shell is made up of 5 orbitals. Hence, 5 d orbitals can store 10 electrons.

A f sub-shell is made up of 7 orbitals. Hence, 7 f orbitals can store 14 electrons.=

Sub-shells Number of OrbitalsNumber of Electrons

s 1 2

p 3 6

d 5 10

f 7 14

Notation of Electric Configuration

There are two methods of notating electric configuration: orbital notation and atomic notation.

Orbital Notation

All electrons can be described by the four quantum numbers, shells, sub-shells or sublevels, orbitals, and spin.

If two electrons have the same four quantum numbers, shells, sub-shells, and orbitals, then they must a different spin. According to the Pauli Exclusion Principle, no two electrons can be the same. Hence, two electrons in an orbital must have opposite spins.

The Aufbau Principle states the lowest energy levels are always filled with electrons first.

The orbitals of sub-shells have the same amount of energy. Therefore, electrons are unpaired as they fill higher energy levels, by Hund Rule.

Orbital Notation

Atomic Notation

Atomic notation is of the form abc, where a is the sub-shell, b is the orbital, and c is the total number of electrons in the orbital.

For further review, look at the Electron Configuration of the Periodic Table section above.

From the periodic table, we can see the arrangement of sub-shells from lowest energy to highest energy:

1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 4d10 4f14

Electron Configuration Analogy: The Address Book

Electron Configuration is an address book for locating electrons. The energy level of an electron is the town (periodic table) an electron resides in. The orbital of an electron is the street (period) on which an electron lives on. The electron spin is the house (box) the electron lives in.